/*
 * Int.c
 * Izracunavanje odredjenog integrala date funkcije f(x) pomocu Simpsonovog pravila
 * Created on: Aug 20, 2010
 * Author: djordje
 */

#include "mpi.h"
#include <stdio.h>
#include <math.h>

const int A = 0;
const int B = 1;
double f( double a )
{
    return (4.0 / (1.0 + a*a));
}

int main( int argc, char *argv[])
{
   long n_intervals = 1000000000;
   long  i;
   int  myid, numprocs;
   double PI25DT = 3.141592653589793238462643;
   double mypi, pi, h, sum;
   double elapsed_time;

   MPI_Init(&argc,&argv);
   MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
   MPI_Comm_rank(MPI_COMM_WORLD,&myid);

   if (myid == 0)
   {
      elapsed_time = -MPI_Wtime();
   }

   h = 1.0 / n_intervals;
   sum = 0.0;
   
   for (i = myid + 1; i <= n_intervals/2; i += numprocs)
   {
       sum += 4 * f((2*i - 1) * h) + 2 * f((2*i) * h);
   }

   MPI_Reduce(&sum, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);

   if (myid == 0)
   {
           elapsed_time += MPI_Wtime();
	   mypi = (f(A) - f(B) + pi) / (3 * n_intervals);
	   printf("Int[%d, %d](f(x)) = %.16f, Error is %.16f\n", A, B, mypi, fabs(mypi - PI25DT));
	   printf("wall clock time = %f\n", elapsed_time);
   }

   MPI_Finalize();

   return 0;
}